Princeton Instruments PI-MAX 3 System, Manual, Page: 43 / 150

Chapter 5 General Operation Factors 43
where
N
x
is the smaller dimension of the CCD
N
y
is the larger dimension of the CCD
t
sr
is the time needed to shift one pixel out of the shift register
t
v
is the time needed to digitize a pixel
t
i
is the time needed to shift one line into the shift register
A subsection of the CCD (number of horizontal pixels must be divisible by 4) can be read
out at full resolution, sometimes dramatically increasing the readout rate while retaining
the highest resolution in the region of interest (ROI). To approximate the readout rate of
an ROI, in Equation 2 substitute the x and y dimensions of the ROI in place of the
dimensions of the full CCD. Some overhead time, however, is required to read out and
discard the unwanted pixels.
The readout rate in frames per second for the PI-MAX3:e2v CCD30-11 1024 × 256 full
frame array running at 2 MHz is shown in Table 2.
Region of Interest Size
Binning
1024 x 256 1024 x 10* 1024 x 1*
1 x 1
6.67
1 x 256 270
1 x 10 1567
1 x 1
1831
* CCD format using Custom Chip mode
Table 2. Spectral Rates for e2v CCD30-11 Array at 2 MHz
Binned Readout (Hardware Binning)
Introduction
Binning is the process of adding the charge from adjacent pixels together to form a single
pixel (sometimes called a super-pixel), and it can be accomplished in either hardware or
software. Rectangular groups of pixels of any size may be binned together, subject to
some hardware and software limitations.
Hardware binning reduces readout time and the burden on computer memory by
summing charge
before the preamplifier reads out the signal. For signal levels that are
readout noise limited this method improves S/N ratio linearly with the number of pixels
grouped together. For signals large enough to render the camera photon shot noise
limited, the S/N ratio improvement is roughly proportional to the square-root of the
number of pixels binned. In the WinX application, hardware binning is set up on the
Acquisition|Experiment Setup…|ROI Setup
tab card by entering a value in the
Group fields: for example, a "2" in each of the Group fields will set up 2 x 2 hardware
binning.